1. Field of the Invention
This invention generally relates to a splined ball screw assembly including a spiral guide channel, which is defined between a pair of inner and outer members and provided with a plurality of balls, and also one or more axial guide channels provided with a plurality of balls so as to allow to provide a relative axial movement between the inner and outer members. More particularly, the present invention relates to a multi-mode splined ball screw assembly which can provide various modes of operation.
2. Description of the Prior Art
A typical prior art splined ball screw assembly is described in the U.S. Pat. No. 3,046,808 and its representative structure is illustrated in FIG. 3. As shown, the splined ball screw assembly generally includes a shaft A which is formed with a ball screw section B and a ball spline section C as located side-by-side in the axial direction of the shaft A. A spiral guide groove and a plurality of axial guide grooves are formed on the same portion of the shaft A. The assembly also includes a nut F which is fitted onto the shaft A with a predetermined gap therebetween and a plurality of balls partly engaged with the spiral guide groove of the shaft A and partly engaged with the spiral guide groove of the nut F. The assembly also includes an outer sleeve G which is located in the axial direction of the shaft A and which includes a plurality of endless guide passages filled with balls which are partly engaged with the respective axial guide grooves of the shaft when located at the load section of the endless guide passage.
With the above-described structure, when the nut F is driven to rotate in either direction through an associated drive gear train, the shaft A is caused to move in either direction along its axial direction without rotation through a spline engagement.
However, in the above-described prior art structure, since the ball screw section B and the ball spline section C are located in a side-by-side relationship in the axial direction, the overall axial length of the completed assembly tends to be large. Thus, there is a limit in making the overall assembly compact in size. In addition, since both of the spiral and axial guide grooves are formed on the same portion of the shaft, processing tends to be complicated and care and high precision are required in processing, so that a relatively long time of period is required and an advanced processing technology is required, which tends to push up the cost. In addition, with this prior art structure, the shaft A can move only in the axial direction and thus the mode of operation is rather limited, which tends to limit the scope of applications.
The inventor proposed an improved splined ball screw assembly and filed a patent application in the U.S.A. on Sept. 4, 1990, U.S. Ser. No. 577,354, claiming the Convention priority from the Japanese U.M. Application No. 1-104099. Although the this splined ball screw assembly is an improvement over the above-described prior art, there still exists room for further improvements, in particular in relation to the mode of operation.